1. Field
The present disclosure relates generally to light emitting-diode (LED) bulbs, and more particularly, to the efficient transfer of heat generated by LEDs in a liquid-filled LED bulb.
2. Related Art
Traditionally, lighting has been generated using fluorescent and incandescent light bulbs. While both types of light bulbs have been reliably used, each suffers from certain drawbacks. For instance, incandescent bulbs tend to be inefficient, using only 2-3% of their power to produce light, while the remaining 97-98% of their power is lost as heat. Fluorescent bulbs, while more efficient than incandescent bulbs, do not produce the same warm light as that generated by incandescent bulbs. Additionally, there are health and environmental concerns regarding the mercury contained in fluorescent bulbs.
Thus, an alternative light source is desired. One such alternative is a bulb utilizing an LED. An LED comprises a semiconductor junction that emits light due to an electrical current flowing through the junction. Compared to a traditional incandescent bulb, an LED bulb is capable of producing more light using the same amount of power. Additionally, the operational life of an LED bulb is orders of magnitude longer than that of an incandescent bulb, for example, 10,000-100,000 hours as opposed to 1,000-2,000 hours.
While there are many advantages to using an LED bulb rather than an incandescent or fluorescent bulb, LEDs have a number of drawbacks that have prevented them from being as widely adopted as incandescent and fluorescent replacements. One drawback is that an LED, being a semiconductor, generally cannot be allowed to get hotter than approximately 120° C. As an example, A-type LED bulbs have been limited to very low power (i.e., less than approximately 8 W), producing insufficient illumination for incandescent or fluorescent replacements.
One potential solution to this problem is to use a large metallic heat sink attached to the LEDs and extending away from the bulb. However, this solution is undesirable because of the common perception that customers will not use a bulb that is shaped radically different from the traditionally shaped A-type form factor bulb. Additionally, the heat sink may make it difficult for the LED bulb to fit into pre-existing fixtures.
Another solution is to fill the bulb with a thermally conductive liquid to transfer heat from the LED to the shell of the bulb. The heat may then be transferred from the shell out into the air surrounding the bulb. However, current liquid-filled LED bulbs do not efficiently transfer heat from the LED to the liquid. Additionally, current liquid-filled LED bulbs do not allow the thermally conductive liquid to flow efficiently to transfer heat from the LED to the shell of the bulb. For example, in a conventional LED bulb having LEDs placed at the base of the bulb structure, the liquid heated by the LEDs rises to the top of the bulb and falls as it cools. However, the liquid does not flow efficiently because the shear force between the liquid rising up and the liquid falling down slows the convective flow of the liquid. Another drawback of current liquid-filled LED bulbs is that they do not efficiently dissipate heat when the bulb is not positioned in an upright orientation. When a conventional LED bulb is placed upside-down, for example, the heat-generating LEDs are flipped from the bottom of the bulb to the top of the bulb. This prevents an efficient convective flow within the bulb because the heated liquid remains at the top of the bulb near the LEDs.
Thus, an LED bulb capable of efficiently transferring heat away from the LEDs, while the LED bulb is in various orientations, is desired.